The backplate part numbers for the Omega B are different to the earlier version used on Omega A/Carlton, Senator B, Calibra and Vectra A, suggesting that they are not interchangeable. So in theory the Senator parts can't be used on your car.
Whether or not they can be modified and made to fit your car is a different matter. You need somebody who has actually done this to confirm.
The modification of inserting the shoe pins from the rear of the backplate applies to the earlier cars as well as Omega B. It's independent of the actual backplate fitted. Hence the revised pins with the cup washers will work on your car but you need to loosen the backplate bolts and move the plate outwards to fit the revised pins. Then move it back and bolt it up again. The bolts require an M10 XZN long (triple square) bit.
For Omega A/ Carlton, Senator B, Calibra & Vectra A
90222355 = LH Rear Brake Flange
90222356 = RH Rear Brake Flange
For Omega B
These are the backplates currently fitted to your car assuming the factory backplates were never previously changed.
90374615 = PLATE,ASSY.,REAR BRAKE CARRIER,LH (NLS.- USE 9156092 5 43 072)
90474616 = PLATE,ASSY.,REAR BRAKE CARRIER,RH (NLS.- USE 9156093 5 43 073)
The backplates were then superseded by these.
9156092 = PLATE,ASSY.,REAR BRAKE CARRIER,LH (NLS.- USE 24436738 5 43 081 AND SUPPLY 24428129 5 43 302,24445691 5 46 211)
9156093 = PLATE,ASSY.,REAR BRAKE CARRIER,RH (NLS.- USE 24436739 5 43 082 AND SUPPLY 24428129 5 43 302,24445691 5 46 211)
The above backplates were then superseded with these.
24436738 = PLATE,ASSY.,REAR BRAKE CARRIER,LH
24436739 = PLATE,ASSY.,REAR BRAKE CARRIER,RH
However to fit the above backplates you also need two each of the below seals.
24428129 = GASKET,PLATE,ASSY.,REAR BRAKE CARRIER
24445691 = BOOT,LEVER,BRAKE CABLE (RUBBER)